Conventional tractor-trailers include a tractor powered by an internal combustion engine and a trailer pulled by the tractor. The internal combustion engine of the tractor drives an axle of the tractor to move the trailer secured to the tractor in an articulated manner. Many tractor-trailers are used to transport cargo over long distances at relatively high rates of speed.
The shape and bulk of traditional tractor-trailers tend to promote the occurrence of aerodynamic drag on the tractor-trailers. Aerodynamic drag is a force that acts on the tractor-trailer in a direction opposing the motion of the tractor-trailer. The total aerodynamic drag on a tractor-trailer includes aerodynamic drag caused by friction between the moving air and the surface of the tractor-trailer, and pressure drag caused by pressure differentials induced by the separation of flow from the tractor-trailer. Aerodynamic drag produces undesirable consequences, such as a reduction in speed, drop in fuel efficiency, increase in operating costs, and the like.
Because of the negative consequences caused by aerodynamic drag, attempts have been made to reduce the drag due to friction drag and pressure drag. Surface finishing techniques have advanced such that friction drag is responsible for only a small portion of the total aerodynamic drag acting on tractor-trailers. In contrast, most techniques aimed at reducing pressure drag fail to adequately mitigate the pressure drag and sufficiently lessen the undesirable consequences of aerodynamic drag.